Experimental and Theoretical Study on Dissociative Photoionization of Cyclopentanone

The dissociative photoionization of cyclopentanone was investigated by means of a reflectron time-of-flight mass spectrometer (RTOF-MS) with tunable vacuum ultraviolet synchrotron radiation in the photon energy range of 9.0-15.5 eV. The photoionization efficiency (PIE) curves for molecular ion and fragment ions were measured. The ionization energy of cyclopentanone was determined to be 9.23\begin{document}$\pm$\end{document}0.03 eV. Fragment ions from the dissociative photoionization of cyclopentanone were identified as C\begin{document}$_5$\end{document}H\begin{document}$_7$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_4$\end{document}H\begin{document}$_5$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_4$\end{document}H\begin{document}$_8^+$\end{document}/C\begin{document}$_3$\end{document}H\begin{document}$_4$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_3$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_4$\end{document}H\begin{document}$_6^+$\end{document}, C\begin{document}$_2$\end{document}H\begin{document}$_4$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_6^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_5^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_4^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_3^+$\end{document}, C\begin{document}$_2$\end{document}H\begin{document}$_5^+$\end{document} and C\begin{document}$_2$\end{document}H\begin{document}$_4^+$\end{document}. With the aid of the ab initio calculations at the \begin{document}$\omega$\end{document}B97X-D/6-31+G(d, p) level of theory, the dissociative mechanisms of C\begin{document}$_5$\end{document}H\begin{document}$_8$\end{document}O\begin{document}$^+$\end{document} are proposed. Ring opening and hydrogen migrations are the predominant processes in most of the fragmentation pathways of cyclopentanone.     

Physical Properties of Si2Ge and SiGe2 in Hexagonal Symmetry: First-Principles Calculations

We predict two novel group 14 element alloys Si\begin{document}$_2$\end{document}Ge and SiGe\begin{document}$_2$\end{document} in \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22 phase in this work through first-principles calculations. The structures, stability, elastic anisotropy, electronic and thermodynamic properties of these two proposed alloys are investigated systematically. The proposed \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-Si\begin{document}$_2$\end{document}Ge and \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-SiGe\begin{document}$_2$\end{document} have a hexagonal symmetry structure, and the phonon dispersion spectra and elastic constants indicate that these two alloys are dynamically and mechanically stable at ambient pressure. The elastic anisotropy properties of \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-Si\begin{document}$_2$\end{document}Ge and \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-SiGe\begin{document}$_2$\end{document} are examined elaborately by illustrating the surface constructions of Young's modulus, the contour surfaces of shear modulus, and the directional dependence of Poisson's ratio; the differences with their corresponding group 14 element allotropes \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-Si\begin{document}$_3$\end{document} and \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-Ge\begin{document}$_3$\end{document} are also discussed and compared. Moreover, the Debye temperature and sound velocities are analyzed to study the thermodynamic properties of the proposed \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-Si\begin{document}$_2$\end{document}Ge and \begin{document}$P$\end{document}6\begin{document}$_2$\end{document}22-SiGe\begin{document}$_2$\end{document}.     

Structures,Energetics, and Infrared Spectra of the Cationic Monomethylamine-Water Clusters

The structures, energetics, and infrared (IR) spectra of the cationic monomethylamine-water clusters, [(CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document})(H\begin{document}$_2$\end{document}O)\begin{document}$_n$\end{document}]\begin{document}$^+$\end{document} (\begin{document}$n$\end{document}=1\begin{document}$-$\end{document}5), have been studied using quantum chemical calculations at the MP2/6-311+G(2d,p) level. The results reveal that the formation of proton-transferred CH\begin{document}$_2$\end{document}NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document} ion core structure is preferred via the intramolecular proton transfer from the methyl group to the nitrogen atom and the water molecules act as the acceptor for the O\begin{document}$\cdots$\end{document}HN hydrogen bonds with the positively charged NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document} moiety of CH\begin{document}$_2$\end{document}NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document}, whose motif is retained in the larger clusters. The CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document}\begin{document}$^+$\end{document} ion core structure is predicted to be less energetically favorable. Vibrational frequencies of CH stretches, hydrogen-bonded and free NH stretches, and hydrogen-bonded OH stretches in the calculated IR spectra of the CH\begin{document}$_2$\end{document}NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document} and CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document}\begin{document}$^+$\end{document} type structures are different from each other, which would afford the sensitive probes for fundamental understanding of hydrogen bonding networks generated from the radiation-induced chemical processes in the [(CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document})(H\begin{document}$_2$\end{document}O)\begin{document}$_n$\end{document}]\begin{document}$^+$\end{document} complexes.     

"Dry" NiCo\begin{document}$_\textbf{2}$\end{document}O\begin{document}$_\textbf{4}$\end{document} Nanorods for Electrochemical Non-enzymatic Glucose Sensing

A rod-like NiCo\begin{document}$_2$\end{document}O\begin{document}$_4$\end{document} modified glassy carbon electrode was fabricated and used for non-enzymatic glucose sensing. The NiCo\begin{document}$_2$\end{document}O\begin{document}$_4$\end{document} was prepared by a facile hydrothermal reaction and subsequently treated in a commercial microwave oven to eliminate the residual water introduced during the hydrothermal procedure. Structural analysis showed that there was no significant structural alteration before and after microwave treatment. The elimination of water residuals was confirmed by the stoichiometric ratio change by using element analysis. The microwave treated NiCo\begin{document}$_2$\end{document}O\begin{document}$_4$\end{document} (M-NiCo\begin{document}$_2$\end{document}O\begin{document}$_4$\end{document}) showed excellent performance as a glucose sensor (sensitivity 431.29 \begin{document}$\mu $\end{document}A\begin{document}$\cdot$\end{document}mmol/L\begin{document}$^{-1}$\end{document}\begin{document}$\cdot$\end{document}cm\begin{document}$^{-2}$\end{document}). The sensing performance decreases dramatically by soaking the M-NiCo\begin{document}$_2$\end{document}O\begin{document}$_4$\end{document} in water. This result indicates that the introduction of residual water during hydrothermal process strongly affects the electrochemical performance and microwave pre-treatment is crucial for better sensory performance.     

Redox Controllable Switch of Crystalline Phase and Physical Property in SrVO\begin{document}$_{x}$\end{document} Epitaxial Films

Transition-metal oxides have attracted much attention due to its abundant crystalline phases and intriguing physical properties. However, some of these compounds are difficult to be fabricated directly in film form due to the ease of valence variation of transition-metal elements. In this work, we reveal the reversible structural transition between SrVO\begin{document}$_3$\end{document} and Sr\begin{document}$_2$\end{document}V\begin{document}$_2$\end{document}O\begin{document}$_7$\end{document} films via thermal treatment in oxygen atmosphere or in vacuum. Based on this, Sr\begin{document}$_2$\end{document}V\begin{document}$_2$\end{document}O\begin{document}$_7$\end{document} epitaxial films are successfully synthesized and studied. Property characterizations show that the semitransparent and metallic SrVO\begin{document}$_3$\end{document} could reversibly switch into transparent and insulating Sr\begin{document}$_2$\end{document}V\begin{document}$_2$\end{document}O\begin{document}$_7$\end{document}, implying potential applications in controllable electronic and optical devices.     

DFT Study on the Catalytic Role of \begin{document}$\alpha$\end{document}-MoC(100) in Methanol Steam Reforming

In this work, we investigated the methanol steam reforming (MSR) reaction (CH\begin{document}$_3$\end{document}OH+H\begin{document}$_2$\end{document}O \begin{document}$\rightarrow$\end{document}CO\begin{document}$_2$\end{document}+3H\begin{document}$_2$\end{document}) catalyzed by \begin{document}$\alpha$\end{document}-MoC by means of density functional theory calculations. The adsorption behavior of the relevant intermediates and the kinetics of the elementary steps in the MSR reaction are systematically investigated. The results show that, on the \begin{document}$\alpha$\end{document}-MoC(100) surface, the O\begin{document}$-$\end{document}H bond cleavage of CH\begin{document}$_3$\end{document}OH leads to CH\begin{document}$_3$\end{document}O, which subsequently dehydrogenates to CH\begin{document}$_2$\end{document}O. Then, the formation of CH\begin{document}$_2$\end{document}OOH between CH\begin{document}$_2$\end{document}O and OH is favored over the decomposition to CHO and H. The sequential dehydrogenation of CH\begin{document}$_2$\end{document}OOH results in a high selectivity for CO\begin{document}$_2$\end{document}. In contrast, the over-strong adsorption of the CH\begin{document}$_2$\end{document}O intermediate on the \begin{document}$\alpha$\end{document}-MoC(111) surface leads to its dehydrogenation to CO product. In addition, we found that OH species, which is produced from the facile water activation, help the O\begin{document}$-$\end{document}H bond breaking of intermediates by lowering the reaction energy barrier. This work not only reveals the catalytic role played by \begin{document}$\alpha$\end{document}-MoC(100) in the MSR reaction, but also provides theoretical guidance for the design of \begin{document}$\alpha$\end{document}-MoC-based catalysts.     

Location Effect in a Photocatalytic Hybrid System of Metal-Organic Framework Interfaced with Semiconductor Nanoparticles

We report an ultrafast spectroscopy investigation that addresses the subtle location effect in a prototypical semiconductor-MOF hybrid system with TiO\begin{document}$_2$\end{document} nanoparticles being incorporated inside or supported onto Cu\begin{document}$_3$\end{document}(BTC)\begin{document}$_2$\end{document}, denoted as TiO\begin{document}$_2$\end{document}@Cu\begin{document}$_3$\end{document}(BTC)\begin{document}$_2$\end{document} and TiO\begin{document}$_2$\end{document}/Cu\begin{document}$_3$\end{document}(BTC)\begin{document}$_2$\end{document}, respectively. By tracking in real time the interface electron dynamics in the hybrid system, we find that the interface states formed between TiO\begin{document}$_2$\end{document} and Cu\begin{document}$_3$\end{document}(BTC)\begin{document}$_2$\end{document} can act as an effective relay for electron transfer, whose efficiency rests on the relative location of the two components. It is such a subtle location effect that brings on difference in photocatalytic CO\begin{document}$_2$\end{document} reduction using the two semiconductor-MOF hybrids. The mechanistic understanding of the involved interface electron-transfer behavior and effect opens a helpful perspective for rational design of MOF-based hybrid systems for photoelectrochemical applications.     

Low-Lying Isomers of (TiO\begin{document}$_{2}$\end{document})\begin{document}$_{n}$\end{document} (\begin{document}${n}$\end{document}=2-8) Clusters

Although there are diverse bond features of Ti and O atoms, so far only several isomers have been reported for each (TiO\begin{document}$_2$\end{document})\begin{document}$_n$\end{document} cluster. Instead of the widely used global optimization, in this work, we search for the low-lying isomers of (TiO\begin{document}$_2$\end{document})\begin{document}$_n$\end{document} (\begin{document}$n$\end{document}=2\begin{document}$-$\end{document}8) clusters with up to 10000 random sampling initial structures. These structures were optimized by the PM6 method, followed by density functional theory calculations. With this strategy, we have located many more low-lying isomers than those reported previously. The number of isomers increases dramatically with the size of the cluster, and about 50 isomers were found for (TiO\begin{document}$_2$\end{document})\begin{document}$_7$\end{document} and (TiO\begin{document}$_2$\end{document})\begin{document}$_8$\end{document} with the energy within kcal/mol. Furthermore, new lowest isomers have been located for (TiO\begin{document}$_2$\end{document})\begin{document}$_5$\end{document} and (TiO\begin{document}$_2$\end{document})\begin{document}$_8$\end{document}, and isomers with three terminal oxygen atoms, five coordinated oxygen atoms as well as six coordinated titanium atoms have been located. Our work highlights the diverse structural features and a large number of isomers of small TiO\begin{document}$_2$\end{document} clusters.     

Imaging Photodissociation Dynamics of MgO at 193 nm

In this work, we used time-sliced ion velocity imaging to study the photodissociation dynamics of MgO at \mbox{193 nm}. Three dissociation pathways are found through the speed and angular distributions of magnesium. One pathway is the one-photon excitation of MgO(X\begin{document}$^1\Sigma^+$\end{document}) to MgO(G\begin{document}$^1\Pi$\end{document}) followed by spin-orbit coupling between the G\begin{document}$^1\Pi$\end{document}, 3\begin{document}$^3\Pi$\end{document} and 1\begin{document}$^5\Pi$\end{document} states, and finally dissociated to the Mg(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{u}$\end{document})+O(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{g}$\end{document}) along the 1\begin{document}$^5\Pi$\end{document} surface. The other two pathways are one-photon absorption of MgO(A\begin{document}$^1\Pi$\end{document}) state to MgO(G\begin{document}$^1\Pi$\end{document}) and MgO(4\begin{document}$^1\Pi$\end{document}) state to dissociate into Mg(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{u}$\end{document})+O(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{g}$\end{document}) and Mg(\begin{document}$^1$\end{document}S\begin{document}$_\textrm{g}$\end{document})+O(\begin{document}$^1$\end{document}S\begin{document}$_\textrm{g}$\end{document}), respectively. The anisotropy parameters of the dissociation pathways are related to the lifetime of the vibrational energy levels and the coupling of rotational and vibronic spin-orbit states. The total kinetic energy analysis gives \begin{document}$D_0$\end{document}(Mg\begin{document}$-$\end{document}O)=21645\begin{document}$\pm$\end{document}50 cm\begin{document}$^{-1}$\end{document}.     

F-(H2O)+CH3I Ligand Exchange Reaction Dynamics

Single hydration of the gas phase F\begin{document}$^-$\end{document}+CH\begin{document}$_3$\end{document}I\begin{document}$\rightarrow$\end{document} I\begin{document}$^-$\end{document}+CH\begin{document}$_3$\end{document}F reaction allows to probe solvent effects on a fundamental nucleophilic substitution reaction. At the same time, the addition of a solvent molecule opens alternative product channels. Here, we present crossed beam imaging results on the dynamics of the F\begin{document}$^-$\end{document}(H\begin{document}$_2$\end{document}O)+CH\begin{document}$_3$\end{document}I\begin{document}$\rightarrow$\end{document}[FCH\begin{document}$_3$\end{document}I]\begin{document}$^-$\end{document}+H\begin{document}$_2$\end{document}O ligand exchange pathway at collision energies between 0.3 and 2.6 eV. Product kinetic energies are constrained by the stability requirement of the weakly bound product complexes. This implies substantial internal excitation of the water molecule and disfavors efficient energy redistribution in an intermediate complex, which is reflected by the suppression of low kinetic energies as collision energy increases. At 0.3 eV, internal nucleophilic displacement is important and is discussed in light of the competing nucleophilic substitution pathways that form I\begin{document}$^-$\end{document} and I\begin{document}$^-$\end{document}(H\begin{document}$_2$\end{document}O).     

Improving Interfacial Electrochemistry of LiNi0.5Mn1.5O4 Cathode Coated by Mn3O4

In this work the surface of LiNi\begin{document}$_{0.5}$\end{document}Mn\begin{document}$_{1.5}$\end{document}O\begin{document}$_{4}$\end{document} (LMN) particles is modified by Mn\begin{document}$_{3}$\end{document}O\begin{document}$_{4}$\end{document} coating through a simple wet grinding method, the electronic conductivity is significantly improved from 1.53\begin{document}$\times$\end{document}10\begin{document}$^{-7}$\end{document} S/cm to 3.15\begin{document}$\times$\end{document}10\begin{document}$^{-5}$\end{document} S/cm after 2.6 wt% Mn\begin{document}$_{3}$\end{document}O\begin{document}$_{4}$\end{document} coating. The electrochemical test results indicate that Mn\begin{document}$_{3}$\end{document}O\begin{document}$_{4}$\end{document} coating dramatically enhances both rate performance and cycling capability (at 55 ℃) of LNM. Among the samples, 2.6 wt% Mn\begin{document}$_{3}$\end{document}O\begin{document}$_{4}$\end{document}-coated LNM not only exhibits excellent rate capability (a large capacity of 108 mAh/g at 10 C rate) but also shows 78% capacity retention at 55 ℃ and 1 C rate after 100 cycles.     

H-Atom Transfer Reaction of Photoinduced Excited Triplet Duroquinone with Tryptophan and Tyrosine in Acetonitrile-Water and Ethylene Glycol-Water Homogeneous Solutions

Laser flash photolysis was used to investigate the photoinduced reactions of excited triplet bioquinone molecule duroquinone (DQ) with tryptophan (Trp) and tyrosine (Tyr) in acetonitrile-water (MeCN-H\begin{document}$_2$\end{document}O) and ethylene glycol-water (EG-H\begin{document}$_2$\end{document}O) solutions. The reaction mechanisms were analyzed and the reaction rate constants were measured based on Stern-Volmer equation. The H-atom transfer reaction from Trp (Tyr) to \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} is dominant after the formation of \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} during the laser photolysis. For DQ and Trp in MeCN-H\begin{document}$_2$\end{document}O and EG-H\begin{document}$_2$\end{document}O solutions, \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} captures H-atom from Trp to generate duroquinone neutral radical DQH\begin{document}$^\bullet$\end{document}, carbon-centered tryptophan neutral radical Trp\begin{document}$^\bullet$\end{document}/NH and nitrogen-centered tryptophan neutral radical Trp/N\begin{document}$^\bullet$\end{document}. For DQ and Tyr in MeCN-H\begin{document}$_2$\end{document}O and EG-H\begin{document}$_2$\end{document}O solutions, \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} captures H-atom from Tyr to generate duroquinone neutral radical DQH\begin{document}$^\bullet$\end{document} and tyrosine neutral radical Tyr/O\begin{document}$^\bullet$\end{document}. The H-atom transfer reaction rate constant of \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} with Trp (Tyr) is on the level of 10\begin{document}$^9$\end{document} L\begin{document}$\cdot$\end{document}mol\begin{document}$^{-1}$\end{document}\begin{document}$\cdot$\end{document}s\begin{document}$^{-1}$\end{document}, nearly controlled by diffusion. The reaction rate constant of \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} with Trp (Tyr) in MeCN/H\begin{document}$_2$\end{document}O solution is larger than that in EG/H\begin{document}$_2$\end{document}O solution, which agrees with Stokes-Einstein relationship qualitatively.     

Reaction Mechanism and Product Branching Ratios of OH+C2H3F Reaction: A Theoretical Study

Ab initio CCSD(T)/CBS//B3LYP/6-311G(d, p) calculations of the potential energy surface for possible dissociation channels of HOC\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F, as well as Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of rate constants, were carried out, in order to predict statistical product branching ratios in dissociation of HOC\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F at various internal energies. The most favorable reaction pathway leading to the major CH\begin{document}$_2$\end{document}CHO+HF products is as the following: OH+C\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F\begin{document}$\rightarrow$\end{document}i2\begin{document}$\rightarrow$\end{document}TS14\begin{document}$\rightarrow$\end{document}i6\begin{document}$\rightarrow$\end{document}TS9\begin{document}$\rightarrow$\end{document}i3\begin{document}$\rightarrow$\end{document}TS3\begin{document}$\rightarrow$\end{document}CH\begin{document}$_2$\end{document}CHO+HF, where the rate-determining step is HF elimination from the CO bridging position via TS11, lying above the reactants by 3.8 kcal/mol. The CH\begin{document}$_2$\end{document}O+CH\begin{document}$_2$\end{document}F products can be formed by F atom migration from C\begin{document}$_\beta$\end{document} to C\begin{document}$_\alpha$\end{document} position via TS14, then H migration from O to C\begin{document}$_\alpha$\end{document} position via TS16, and C-C breaking to form the products via TS5, which is 1.8 kcal/mol lower in energy than the reactants, and 4.0 kcal/mol lower than TS11.     

Ag-Cu Nanoparticles Supported on N-Doped TiO\begin{document}$_2$\end{document} Nanowire Arrays for Efficient Photocatalytic CO\begin{document}$_2$\end{document} Reduction

Photocatalytic reduction of CO\begin{document}$_2$\end{document} into various types of fuels has attracted great interest, and serves as a potential solution to addressing current global warming and energy challenges. In this work, Ag-Cu nanoparticles are densely supported on N-doped TiO\begin{document}$_2$\end{document} nanowire through a straightforward nanofabrication approach. The range of light absorption by N-doped TiO\begin{document}$_2$\end{document} can be tuned to match the plasmonic band of Ag nanoparticles, which allows synergizing a resonant energy transfer process with the Schottky junction. Meanwhile, Cu nanoparticles can provide active sites for the reduction of CO\begin{document}$_2$\end{document} molecules. Remarkably, the performance of photocatalytic CO\begin{document}$_2$\end{document} reduction is improved to produce CH\begin{document}$_4$\end{document} at a rate of 720 \begin{document}$\mu$\end{document}mol\begin{document}$\cdot$\end{document}g\begin{document}$^{-1}$\end{document}\begin{document}$\cdot$\end{document}h\begin{document}$^{-1}$\end{document} under full-spectrum irradiation.     

Atomistic Mechanisms for Catalytic Transformations of NO to NH3, N2O,and N2 by Pd

The industrial pollutant NO is a potential threat to the environment and to human health. Thus, selective catalytic reduction of NO into harmless N\begin{document}$_2$\end{document}, NH\begin{document}$_3$\end{document}, and/or N\begin{document}$_2$\end{document}O gas is of great interest. Among many catalysts, metal Pd has been demonstrated to be most efficient for selectivity of reducing NO to N\begin{document}$_2$\end{document}. However, the reduction mechanism of NO on Pd, especially the route of N\begin{document}$-$\end{document}N bond formation, remains unclear, impeding the development of new, improved catalysts. We report here the elementary reaction steps in the reaction pathway of reducing NO to NH\begin{document}$_3$\end{document}, N\begin{document}$_2$\end{document}O, and N\begin{document}$_2$\end{document}, based on density functional theory (DFT)-based quantum mechanics calculations. We show that the formation of N\begin{document}$_2$\end{document}O proceeds through an Eley-Rideal (E-R) reaction pathway that couples one adsorbed NO\begin{document}$^*$\end{document} with one non-adsorbed NO from the solvent or gas phase. This reaction requires high NO\begin{document}$^*$\end{document} surface coverage, leading first to the formation of the trans-(NO)\begin{document}$_2$\end{document}\begin{document}$^*$\end{document} intermediate with a low N\begin{document}$-$\end{document}N coupling barrier (0.58 eV). Notably, trans-(NO)\begin{document}$_2$\end{document}\begin{document}$^*$\end{document} will continue to react with NO in the solvent to form N\begin{document}$_2$\end{document}O, that has not been reported. With the consumption of NO and the formation of N\begin{document}$_2$\end{document}O\begin{document}$^*$\end{document} in the solvent, the Langmuir-Hinshelwood (L-H) mechanism will dominate at this time, and N\begin{document}$_2$\end{document}O\begin{document}$^*$\end{document} will be reduced by hydrogenation at a low chemical barrier (0.42 eV) to form N\begin{document}$_2$\end{document}. In contrast, NH\begin{document}$_3$\end{document} is completely formed by the L-H reaction, which has a higher chemical barrier (0.87 eV). Our predicted E-R reaction has not previously been reported, but it explains some existing experimental observations. In addition, we examine how catalyst activity might be improved by doping a single metal atom (M) at the NO\begin{document}$^*$\end{document} adsorption site to form M/Pd and show its influence on the barrier for forming the N\begin{document}$-$\end{document}N bond to provide control over the product distribution.     

Substituent Effects on the Photocatalytic Properties of a Symmetric Covalent Organic Framework

Symmetric covalent organic framework (COF) photocatalysts generally suffer from inefficient charge separation and short-lived photoexcited states. By performing density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, we find that partial substitution with one or two substituents (N or NH\begin{document}$_2$\end{document}) in the linkage of the representative symmetric COF (N\begin{document}$_0$\end{document}-COF) gives rise to the separation of charge carriers in the resulting COFs (\emph{i.e}., N\begin{document}$_1$\end{document}-COF, N\begin{document}$_2$\end{document}-COF, (NH\begin{document}$_2$\end{document})\begin{document}$_1$\end{document}-N\begin{document}$_0$\end{document}-COF, and (NH\begin{document}$_2$\end{document})\begin{document}$_2$\end{document}-N\begin{document}$_0$\end{document}-COF). Moreover, we also find that the energy levels of the highest occupied crystal orbital (HOCO) and the lowest unoccupied crystal orbital (LUCO) of the N\begin{document}$_0$\end{document}-COF can shift away from or toward the vacuum level, depending on the electron-withdrawing or electron-donating characters of the substituent. Therefore, we propose that partial substitution with carefully chosen electron-withdrawing or electron-donating substituents in the linkages of symmetric COFs can lead to efficient charge separation as well as appropriate HOCO and LUCO positions of the generated COFs for specific photocatalytic reactions. The proposed rule can be utilized to further boost the photocatalytic performance of many symmetric COFs.     

3D Macro-Micro-Mesoporous FeC\begin{document}$_{2}$\end{document}O\begin{document}$_{4}$\end{document}/Graphene Hydrogel Electrode for High-Performance 2.5 V Aqueous Asymmetric Supercapacitors

Distinguished from commonly used Fe\begin{document}$_2$\end{document}O\begin{document}$_3$\end{document} and Fe\begin{document}$_3$\end{document}O\begin{document}$_4$\end{document}, a three-dimensional multilevel macro-micro-mesoporous structure of FeC\begin{document}$_2$\end{document}O\begin{document}$_4$\end{document}/graphene composite has been prepared as binder-free electrode for supercapacitors. The as-prepared materials are composed of macroporous graphene and microporous/mesoporous ferrous oxalate. Generally, the decomposition voltage of water is 1.23 V and the practical voltage window limit is about 2 V for asymmetric supercapacitors in aqueous electrolytes. When FeC\begin{document}$_2$\end{document}O\begin{document}$_4$\end{document}/rGO hydrogel was used as the negative electrode and a pure rGO hydrogel was used as the positive electrode, the asymmetrical supercapacitor voltage window raised to 1.7 V in KOH (1.0 mol/L) electrolyte and reached up to 2.5 V in a neutral aqueous Na\begin{document}$_2$\end{document}SO\begin{document}$_4$\end{document} (1.0 mol/L) electrolyte. Correspondingly it also exhibits a high performance with an energy density of 59.7 Wh/kg. By means of combining a metal oxide that owns micro-mesoporous structure with graphene, this work provides a new opportunity for preparing high-voltage aqueous asymmetric supercapacitors without addition of conductive agent and binder.     

Enhanced Crystal Quality of Perovskite via Protonated Graphitic Carbon Nitride Added in Carbon-Based Perovskite Solar Cells

The quality of perovskite layers has a great impact on the performance of perovskite solar cells (PSCs). However, defects and related trap sites are generated inevitably in the solution-processed polycrystalline perovskite films. It is meaningful to reduce and passivate the defect states by incorporating additive into the perovskite layer to improve perovskite crystallization. Here an environmental friendly 2D nanomaterial protonated graphitic carbon nitride (p-g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document}) was successfully synthesized and doped into perovskite layer of carbon-based PSCs. The addition of p-g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document} into perovskite precursor solution not only adjusts nucleation and growth rate of methylammonium lead tri-iodide (MAPbI\begin{document}$_3$\end{document}) crystal for obtaining flat perovskite surface with larger grain size, but also reduces intrinsic defects of perovskite layer. It is found that the p-g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document} locates at the perovskite core, and the active groups -NH\begin{document}$_2$\end{document}/NH\begin{document}$_3$\end{document} and NH have a hydrogen bond strengthening, which effectively passivates electron traps and enhances the crystal quality of perovskite. As a result, a higher power conversion efficiency of 6.61% is achieved, compared with that doped with g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document} (5.93%) and undoped one (4.48%). This work demonstrates a simple method to modify the perovskite film by doping new modified additives and develops a low-cost preparation for carbon-based PSCs.     

Electrosynthesis of Highly Efficient WO\begin{document}$_{3-x}$\end{document}/Graphene (Photo-)Electro- Catalyst by Two-Electrode Electrolysis System for Oxygen Evolution Reaction

Integration of non-noble transition metal oxides with graphene is known to construct high-activity electrocatalysts for oxygen evolution reduction (OER). In order to avoid the complexity of traditional synthesis process, a facile electrochemical method is elaborately designed to engineer efficient WO\begin{document}$_{3-x}$\end{document}/graphene (photo-)electrocatalyst for OER by a two-electrode electrolysis system, where graphite cathode is exfoliated into graphene and tungsten wire anode evolves into V\begin{document}$_\textrm{O}$\end{document}-rich WO\begin{document}$_{3-x}$\end{document} profiting from formed reductive electrolyte solution. Among as-prepared samples, WO\begin{document}$_{3-x}$\end{document}/G-2 shows the best electrocatalytic performance for OER with an overpotential of 320 mV (without iR compensation) at 10 mA/cm\begin{document}$^2$\end{document}, superior to commercial RuO\begin{document}$_2$\end{document} (341 mV). With introduction of light illumination, the activity of WO\begin{document}$_{3-x}$\end{document}/G-2 is greatly enhanced and its overpotential decreases to 290 mV, benefiting from additional reaction path produced by photocurrent effect and extra active sites generated by photogenerated carriers (h\begin{document}$^+$\end{document}). Characterization results indicate that both V\begin{document}$_\textrm{O}$\end{document}-rich WO\begin{document}$_{3-x}$\end{document} and graphene contribute to the efficient OER performance. The activity of WO\begin{document}$_{3-x}$\end{document} for OER is decided by the synergistic effect between V\begin{document}$_\textrm{O}$\end{document} concentration and particle size. The graphene could not only disperse WO\begin{document}$_{3-x}$\end{document} nanoparticles, but also improve the holistic conductivity and promote electron transmission. This work supports a novel method for engineering WO\begin{document}$_{3-x}$\end{document}/graphene composite for highly efficient (photo-)electrocatalytic performance for OER.     

Effect of a Single Repeat Sequence of the Human Telomere d(TTAGGG) on Structure of Single-Stranded Telomeric DNA d[AGGG(TTAGGG)\begin{document}$_6$\end{document}]

The structures of human telomeric DNA have received much attention due to its significant biological importance. Most studies have focused on G-quadruplex structure formed by short telomeric DNA sequence, but little is known about the structures of long single-stranded telomeric DNAs. Here, we investigated the structure of DNA with a long sequence of d[AGGG(TTAGGG)\begin{document}$_6$\end{document}] (G\begin{document}$_6$\end{document}-DNA) and the effect of a single repeat sequence d(TTAGGG) (G\begin{document}$_{01}$\end{document}-DNA) on the structure of G\begin{document}$_6$\end{document}-DNA using sedimentation velocity technique, polyacrylamide gel electrophoresis, circular dichroism spectroscopy, and UV melting experiments. The results suggest that the G\begin{document}$_6$\end{document}-DNA can form dimers in aqueous solutions and G\begin{document}$_{01}$\end{document}-DNA can form additional G-quadruplex structures by binding to G\begin{document}$_6$\end{document}-DNA. However, G\begin{document}$_{01}$\end{document}-DNA has no effect on the structure of DNA with a sequence of d[AGGG(TTAGGG)\begin{document}$_3$\end{document}] (G\begin{document}$_3$\end{document}-DNA). Our study provides new insights into the structure polymorphism of long human single-stranded telomeric DNA.